Methanol is a valuable substance that has a major role in the chemical industry, environmental sciences, and energy generation. Methanol is a readily transportable source of hydrogen, and it can be selectively oxidized to produce chemicals that are useful to the pharmaceutical sector. Methyl formate, which is helpful for the manufacturing of several valuable chemicals, is one of the many value-added commodity chemicals that can be produced from methanol. Nevertheless, it is still unclear exactly which chemical pathways methanol oxidation catalysts follow. A fundamental understanding of the reaction pathways is necessary for developing innovative catalyst design strategies.
Titania-supported noble metals are excellent candidate materials for accelerating the coupling or oxidation of methanol. Particularly, Pt/TiO2 is active in coupling-type reactions that produce compounds like methyl formate. It has been established that the transfer of electrons between Pt and TiO2 through electronic metal-support interaction (EMSI) is greatly influenced by the size of Pt nanoparticle and its local coordination environment, including both Pt-Pt and Pt-O coordination.
In this work we investigate a Pt/TiO2 system with Pt nanoparticles of size 0.9 nm and its reactivity towards methanol oxidation. As the size of the cluster increases, the degree of freedom in which the cluster can rearrange and interact with the surface increases exponentially. Especially in reaction conditions, the structure of the catalyst may still change. We explored the stability of Pt6Ox supported on anatase TiO2 and all of its accessible metastable states under reaction condition using the grand canonical basin hopping algorithm.
The partial and total oxidation of methanol over a Pt6Ox/TiO2 catalyst has been studied by periodic density functional theory calculations within the generalized gradient approximation. Intermediates seen are formates, dioxymethylene (DOM), and CO. Reaction paths including the geometry and the energetics of several reaction intermediates and the activation barriers between them have been determined, thus developing a fundamental mechanistic understanding of methanol oxidation on this system. DFT simulations and experimental data demonstrate that methyl formate is produced under mild reaction conditions, and full combustion to CO2 is attained. Through a series of proton-coupled electron-transfer processes, CO2 is produced via a surface-bound formate intermediate.
These results provide valuable insight into potential modifications that could preferentially guide catalyst activity toward partial or full oxidation, thereby opening up new avenues for the production of lucrative commodity chemicals. Overall, our findings demonstrate the rich chemistry of metal-support oxide interfaces and the importance of cluster for higher reactivity towards methanol oxidation.